Okay, so I dont know is exact location, but for all you Zelda fanatics out there, you should know who I'm talking about. There is a guy, and when you go talk to him, nothing comes up. Just a bunch of periods. He's standing next to a sign that states to basically ignore him and to leave him alone. However, you take his sign, he chases you around. Is he anything important and if he is, what do I do with him.

when you come across a certain chest that if i remember right has the key inside it and is locked you take it to him and he will unlock it, and then you get another jar.

After you beat the Ice Palace, you go to the building where the the smithys are. In the broken down building there is a purple chest. Take it, use the magic mirror to go back to light world, and take it to him. He'll tell you that he used to be a thief, then tells you that he'll open it if you promise not to tell. In the chest is another bottle. Assuming you have the other 3, that makes 4.

He use to be a thief.

I can't remember if this is correct or I'm just confusing him but I think he was a thief in the Dark World and returned. Someone please correct me if I'm wrong or post if I'm entirely correct.

Otherwise, he was just a thief that gives you the fourth bottle.